Self-regulation of phytoalexin production: a non-biosynthetic enzyme controls alkaloid biosynthesis in cultured cells of Eschscholzia californica
Self-regulation of phytoalexin production: a non-biosynthetic enzyme controls alkaloid biosynthesis in cultured cells of Eschscholzia californica
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DOI：
10.1007/s11240-014-0565-6
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发表时间：
2014-07
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通讯作者：
H. Müller;M. Heinze;Ramona Heinke;Jürgen Schmidt;W. Roos
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作者：
H. Müller;M. Heinze;Ramona Heinke;Jürgen Schmidt;W. Roos
苯并菲啶类生物碱是罂粟科植物中的强抗菌剂，也是药物开发的重要先导化合物。这些化合物的细胞毒性要求生产植物限制病原体触发的生物合成爆发。细胞分泌早期的benzophenanthridines到细胞壁，然后通过解毒酶血根碱还原酶在细胞质中再摄取和还原。我们现在发现这种酶是生物碱生产中自我控制的核心成分。基于RNAi的血根碱还原酶的沉默产生了突变体，其显示激发子触发的生物碱产生的完全停止或生物合成的爆发，其数倍于野生型水平。这些意想不到的表型反映了血根碱还原酶的底物或产物的影响：底物血根碱抑制质膜上的磷脂酶A2，磷脂酶A2是生物合成酶表达信号通路的初始组分。该产品，二氢血根碱，抑制酶的早期生物合成，在牛心果碱形成。通过调节这些稳定状态，血根碱还原酶调节生物碱生物合成的能力：最低活性足以防止血根碱阻断诱导途径，而相同酶的全部活性导致通过二氢血根碱的生物合成流的限制。
Benzophenanthridine alkaloids are strong antimicrobials of Papaveraceae and attractive lead compounds for drug development. The cytotoxicity of these compounds requires the producing plant to limit the pathogen-triggered burst of biosynthesis. Cells ofEschscholzia californicaexcrete early benzophenanthridines to the cell wall, followed by re-uptake and reduction in the cytoplasm by the detoxifying enzyme sanguinarine reductase. We now discovered that this enzyme is a core component of self-control in alkaloid production. RNAi-based silencing of sanguinarine reductase gave rise to mutants that either show a complete stop of elicitor-triggered alkaloid production or a burst of biosynthesis that severalfold surpasses the wild type level. These unexpected phenotypes reflect impacts of substrate or product of sanguinarine reductase: the substrate, sanguinarine, inhibits phospholipase A2 at the plasma membrane, an initial component of the signal path towards expression of biosynthetic enzymes. The product, dihydrosanguinarine, inhibits enzymes of early biosynthesis, prior to reticuline formation. By tuning these steady states, sanguinarine reductase adjusts the capacity of alkaloid biosynthesis: a minimum activity is sufficient to prevent the blockade of the induction pathway by sanguinarine, while the full activity of the same enzyme causes a limitation of the biosynthetic flow via dihydrosanguinarine.